U.S. patent number 5,633,037 [Application Number 07/956,765] was granted by the patent office on 1997-05-27 for multicoat refinishing process.
This patent grant is currently assigned to BASF Lacke + Farben, AG. Invention is credited to Bernd Mayer.
United States Patent |
5,633,037 |
Mayer |
May 27, 1997 |
Multicoat refinishing process
Abstract
The subject matter of the present invention is a multicoat
metallic refinishing process in which a coating material is first
applied to the prepared area of damage and to the adjacent regions
of original finish. A metallic basecoat is applied to this first
coating in such a way that the basecoat hides the area of damage
and tapers off on the coating. A clearcoat is then applied to the
basecoat and, if appropriate, also to the adjacent regions of the
original finish. In the process an aqueous metallic basecoat and an
aqueous coating material containing a) 5 to 50% by weight, based on
the total weight of the coating material, of at least one
water-thinnable or water-dispersible film-forming material, b) 0 to
20% by weight, based on the total weight of the coating material,
of at least one organic solvent c) conventional auxiliaries and
additives, if appropriate, are applied to the prepared area of
damage, the dry film thickness of this aqueous coating material
being between 2 and 50 .mu.m in the region of the area of
damage.
Inventors: |
Mayer; Bernd (Munster,
DE) |
Assignee: |
BASF Lacke + Farben, AG
(Muenster-Hiltrup, DE)
|
Family
ID: |
6402682 |
Appl.
No.: |
07/956,765 |
Filed: |
April 22, 1994 |
PCT
Filed: |
March 06, 1991 |
PCT No.: |
PCT/EP91/00416 |
371
Date: |
April 22, 1994 |
102(e)
Date: |
April 22, 1994 |
PCT
Pub. No.: |
WO91/14513 |
PCT
Pub. Date: |
October 03, 1991 |
Foreign Application Priority Data
|
|
|
|
|
Mar 21, 1990 [DE] |
|
|
40 09 000.0 |
|
Current U.S.
Class: |
427/140; 427/142;
427/409 |
Current CPC
Class: |
B05D
5/005 (20130101); B05D 5/068 (20130101); B05D
7/572 (20130101); C08G 18/0819 (20130101); C09D
5/02 (20130101) |
Current International
Class: |
B05D
5/06 (20060101); B05D 7/00 (20060101); B05D
5/00 (20060101); C08G 18/08 (20060101); C08G
18/00 (20060101); C09D 5/02 (20060101); B32B
035/00 (); B05D 001/36 () |
Field of
Search: |
;427/140,142,409,410,421,412.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Derwent Abstract 89-329285/45 of JO 1245-882-A, Oct. 1989, Nissan
Motor KK. .
Derwent Abstract 54098C/31 of JA 0079075, Jun. 1980, Toyo Kogyo
KK..
|
Primary Examiner: Dudash; Diana
Attorney, Agent or Firm: Sabourin; Anne Gerry
Claims
I claim:
1. A multicoat refinishing process for repairing an area of damage
of an original finish, in which
A) the area of damage is prepared for the application of a refinish
paint system by cleaning, sanding, and, if necessary, applying a
surfacer and/or body filler,
B) a first coating material is applied to the prepared area of
damage and to an adjacent original finish area,
C) a first coating film, having a dry film thickness of between 2
and 50 .mu.m in the area of damage, is formed from the first
coating material,
D) an aqueous basecoat composition containing metallic and/or
special-effect pigments is applied to the first coating film at
such a thickness that the basecoat composition hides the area of
damage and has a dry film thickness that gradually diminishes
outwards from the edge of the area of damage to 0 .mu.m within the
adjacent region of the original finish coated with the first
coating film,
E) a basecoat film is formed from the basecoat composition,
F) a transparent topcoat composition is applied to the basecoat
film, and then
G) a topcoat film is formed from the topcoat composition and the
topcoat, basecoat, and first coating layers are dried together at a
temperature between room temperature and 100.degree. C.,
wherein
I) the first coating material is aqueous and comprises
a) 5 to 50% by weight, based on the total weight of the coating
material, of at least one water-thinnable or water-dispersible
film-forming material,
b) 0 to 20% by weight, based on the total weight of the coating
material, of at least one organic solvent, and
wherein
the first coating material and/or the basecoat compositions contain
resins selected from the group consisting of polyurethane resins,
emulsion polymers obtained by
(a) polymerizing in the first stage 10 to 90 parts by weight of an
ethylenically unsaturated monomer or a mixture of ethylenically
unsaturated monomers in aqueous phase in the presence of one or
more emulsifiers and one or more radical-forming initiators, the
ethylenically unsaturated monomer or the mixture of ethylenically
unsaturated monomers being chosen so that in the first stage a
polymer is obtained having a glass transition temperature
(T.sub.G1) of +30.degree. to +110.degree. C., and,
(b) after at least 80% by weight of the ethylenically unsaturated
monomer or monomer mixture used in the first stage has reacted,
polymerizing in a second stage 90 to 10 parts by weight of an
ethylenically unsaturated monomer or a mixture of ethylenically
unsaturated monomers in the presence of the polymer obtained in the
first stage, the monomer used in the second stage or the mixture of
ethylenically unsaturated monomers used in the second stage being
chosen so that a sole polymerization of the monomer used in the
second stage or of the mixture of ethylenically unsaturated
monomers used in the second stage furnishes a polymer having a
glass transition temperature (T.sub.G2) of -60.degree. to
+20.degree. C., and the reaction conditions being chosen so that
the resultant emulsion polymer had a number average molecular
weight of 200,00 to 2,000,000, and the ethylenically unsaturated
monomer or mixture of monomers used in the first stage and those of
the ethylenically unsaturated monomer or mixture of monomers used
in the second stage being chosen so that the resultant emulsion
polymer has a hydroxyl value of 2 to 100 and the difference
(T.sub.G1)-(T.sub.G2) is 10.degree. to 170.degree. C.
2. The process as claimed in claim 1, wherein the first coating
film has a dry film thickness in the area of original finish that
gradually diminishes outwards from the edge of the area of damage
to 0 .mu.m.
3. The process as claimed in claim 2, wherein the dry film
thickness of the first coating film diminishes to a dry film
thickness of 0 .mu.m in a region of the original finish between 1
cm and 1 m wide.
4. The process as claimed in claim 1, wherein the transparent
topcoat film has a dry film thickness in the adjacent region of the
original finish that gradually diminishes outwards from the edge of
the area of damage to 0 .mu.m.
5. The process as claimed in claim 1, wherein the transparent
topcoat composition is applied extending into the adjacent region
of the original finish until a boundary of the original finish is
reached.
6. The process as claimed in claim 1, wherein the first coating
material and/or the basecoat composition contain as the
film-forming material an emulsion polymer obtained by
(a) polymerizing in a first stage 10 to 90 parts by weight of an
ethylenically unsaturated monomer or a mixture of ethylenically
unsaturated monomers in aqueous phase in the presence of one or
more emulsifiers and one or more radical-forming initiators, the
ethylenically unsaturated monomer or the mixture of ethylenically
unsaturated monomers being chosen so that in the first stage a
polymer is obtained having a glass transition temperature
(T.sub.G1) of +30.degree. to 110.degree. C., and,
(b) after at least 80% by weight of the ethylenically unsaturated
monomer or monomer mixture used in the first stage has reacted,
polymerizing in a second stage 90 to 10 parts by weight of an
ethylenically unsaturated monomer or a mixture of ethylenically
unsaturated monomers in the presence of the polymer obtained in the
first stage, the monomer used in the second stage or the mixture of
ethylenically unsaturated monomers used in the second stage being
chosen so that a sole polymerization of the monomer used in the
second stage or of the mixture of ethylenically unsaturated
monomers used in the second stage furnishes a polymer having a
glass transition temperature (T.sub.G2) of -60.degree. to
+20.degree. C., and the reaction conditions being chosen so that
the resultant emulsion polymer has a number average molecular
weight of 200,000 to 2,000,000, the ethylenically unsaturated
monomer or mixture of monomers used in the first stage and those of
the ethylenically unsaturated monomer or mixture of monomers used
in the second stage being chosen so that the resultant emulsion
polymer has a hydroxyl value of 2 to 100 and the difference
T.sub.G1 -T.sub.G2 is 10.degree. to 170.degree. C.
7. The process as claimed in claim 6, wherein the first coating
material and/or the basecoat composition contains as the
film-forming material a mixture consisting of at least 40% by
weight of the emulsion polymer and up to 60% by weight of a
water-thinnable polyurethane resin, the amounts in each case being
based on the solids content and their sum always being 100% by
weight.
8. The process as claimed in claim 1, wherein the first coating
material and/or the basecoat composition contain as the
film-forming material a water-thinnable or water-dispersible
polyurethane resin.
9. The process as claimed in claim 1, wherein the area of damage is
prepared by applying an aqueous surfacer and/or body filler.
10. A multicoat refinishing process for repairing an area of damage
of an original finish, wherein
A) the area of damage is prepared for the application of a refinish
paint system by cleaning, sanding, and, if necessary, applying a
surfacer and/or body filler,
B) a first coating material is applied to the prepared area of
damage and to adjacent original finish areas until a boundary of
the original finish is reached,
C) a first coating film, having a dry film thickness of between 2
and 50 .mu.m in the area of damage, is formed from the first
coating material,
D) a basecoat composition containing metallic and/or special-effect
pigments is applied to the first coating film,
E) a basecoat film is formed from the basecoat composition,
F) a transparent topcoat composition is applied to the basecoat
film, and then
G) a topcoat film is formed from the topcoat composition and the
topcoat, basecoat, and first coating layers are dried together at a
temperature between room temperature and 140.degree. C.,
wherein
I) the first coating material is aqueous and comprises
a) 5 to 50% by weight, based on the total weight of the coating
material, of at least one water-thinnable or water-dispersible
film-former,
b) 0 to 20% by weight, based on the total weight of the coating
material, of at least one organic solvent, and
II) the basecoat composition is aqueous.
11. The process as claimed in claim 10, wherein the aqueous first
coating material contains coloring pigments, except metallic and
special-effect pigments.
12. The process as claimed in claim 10, wherein the first coating
material and/or the basecoat composition contain as the
film-forming material an emulsion polymer obtained by
(a) polymerizing in the first stage 10 to 90 parts by weight of an
ethylenically unsaturated monomer or a mixture of ethylenically
unsaturated monomers in aqueous phase in the presence of one or
more emulsifiers and one or more radical-forming initiators, the
ethylenically unsaturated monomer or the mixture of ethylenically
unsaturated monomers being chosen so that in the first stage a
polymer is obtained having a glass transition temperature
(T.sub.G1) of +30.degree. to 110.degree. C., and,
(b) after at least 80% by weight of the ethylenically unsaturated
monomer or monomer mixture used in the first stage has reacted,
polymerizing in a second stage 90 to 10 parts by weight of an
ethylenically unsaturated monomer or a mixture of ethylenically
unsaturated monomers in the presence of the polymer obtained in the
first stage, the monomer used in the second stage or the mixture of
ethylenically unsaturated monomers used in the second stage being
chosen so that a sole polymerization of the monomer used in the
second stage or of the mixture of ethylenically unsaturated
monomers used in the second stage furnishes a polymer having a
glass transition temperature (T.sub.G2) of -60.degree. to
+20.degree. C., and the reaction conditions being chosen so that
the resultant emulsion polymer has a number average molecular
weight of 200,000 to 2,000,000, the ethylenically unsaturated
monomer or mixture of monomers used in the first stage and those of
the ethylenically unsaturated monomer or mixture of monomers used
in the second stage being chosen so that the resultant emulsion
polymer has a hydroxyl value of 2 to 100 and the difference
T.sub.G1 -T.sub.G2 is 10.degree. to 170.degree. C.
13. The process as claimed in claim 2, wherein the first coating
material and/or the basecoat composition contains as the
film-forming material a mixture consisting of at least 40% by
weight of the emulsion polymer and up to 60% by weight of a
water-thinnable polyurethane resin, the amounts in each case being
based on the solids content and their sum always being 100% by
weight.
14. The process as claimed in claim 10, wherein the first coating
material and/or the basecoat composition contain as the
film-forming material a water-thinnable or water-dispersible
polyurethane resin.
15. The process as claimed in claim 10, wherein the area of damage
is prepared by applying an aqueous surfacer and/or body filler.
16. A multicoat refinishing process for repairing an area of damage
of an original finish, wherein
A) the area of damage is prepared for the application of a refinish
paint system by cleaning, sanding, and, if necessary, applying a
surfacer and/or body filler,
B) a first coating material is applied to the prepared area of
damage and to adjacent original finish areas until a boundary of
the original finish is reached,
C) a first coating film, having a dry film thickness of between 2
and 50 .mu.m in the area of damage, is formed from the first
coating material,
D) an aqueous basecoat composition containing metallic and/or
special-effect pigments is applied to the first coating film,
E) a basecoat film is formed from the basecoat composition,
F) a transparent topcoat composition is applied to the basecoat
film, and then
G) a topcoat film is formed from the topcoat composition and the
topcoat, basecoat, and first coating layers are dried together at a
temperature between room temperature and 140.degree. C.,
wherein
I) the first coating material is aqueous and comprises
a) 5 to 50% by weight, based on the total weight of the coating
material, of at least one water-thinnable or water-dispersible
film-former,
b) 0 to 20% by weight, based on the total weight of the coating
material, of at least one organic solvent, and
wherein
the first coating material and/or the basecoat compositions contain
water-dispersible film-formers comprising emulsion polymers
obtained by
(a) polymerizing in the first stage 10 to 90 parts by weight of an
ethylenically unsaturated monomer or a mixture of ethylenically
unsaturated monomers in aqueous phase in the presence of one or
more emulsifiers and one or more radical-forming initiators, the
ethylenically unsaturated monomer or the mixture of ethylenically
unsaturated monomers being chosen so that in the first stage a
polymer is obtained having a glass transition temperature
(T.sub.G1) of +30.degree. to +110.degree. C., and,
(b) after at least 80% by weight of the ethylenically unsaturated
monomer or monomer mixture used in the first stage has reacted,
polymerizing in a second stage 90 to 10 parts by weight of an
ethylenically unsaturated monomer or a mixture of ethylenically
unsaturated monomers in the presence of the polymer obtained in the
first stage, the monomer used in the second stage or the mixture of
ethylenically unsaturated monomers used in the second stage being
chosen so that a sole polymerization of the monomer used in the
second stage or of the mixture of ethylenically unsaturated
monomers used in the second stage furnishes a polymer having a
glass transition temperature (T.sub.G2) of -60.degree. to
+20.degree. C., and the reaction conditions being chosen so that
the resultant emulsion polymer had a number average molecular
weight of 200,00 to 2,000,000, and the ethylenically unsaturated
monomer or mixture of monomers used in the first stage and those of
the ethylenically unsaturated monomer or mixture of monomers used
in the second stage being chosen so that the resultant emulsion
polymer has a hydroxyl value of 2 to 100 and the difference
(T.sub.G1)-(T.sub.G2) is 10.degree. to 170.degree. C., and mixtures
of polyurethane polymers and said emulsion polymers.
17. The process as claimed in claim 16, wherein the basecoat
composition applied in step D) containing metallic and/or
special-effect pigments is applied to the first coating film at
such a thickness that the basecoat composition hides the area of
damage and has a dry film thickness that gradually diminishes
outwards from the edge of the area of damage to 0 .mu.m within the
adjacent region of the original finish coated with the first
coating film.
18. The process as claimed in claim 16, wherein the first coating
material and/or the basecoat composition contains as the
film-forming material a mixture consisting of at least 40% by
weight of the emulsion polymer and up to 60% by weight of a
water-thinnable polyurethane resin, the amounts in each case being
based on the solids content and their sum always being 100% by
weight.
19. The process as claimed in claim 17, wherein the first coating
material and/or the basecoat composition contains as the
film-forming material a mixture consisting of at least 40% by
weight of the emulsion polymer and up to 60% by weight of a
water-thinnable polyurethane resin, the amounts in each case being
based on the solids content and their sum always being 100% by
weight.
Description
The subject matter of the present invention is a multicoat
refinishing process in which
1.) the area of damage is prepared for the application of a
refinish paint system by cleaning, sanding and, if necessary,
applying a surfacer and/or body filler,
2.) a coating material is applied to the prepared area of damage
and to the adjacent original finish areas,
3.) a polymeric film is formed from the coating material applied in
stage (2),
4.) a basecoat composition containing metallic and/or
special-effect pigments is applied to the coating obtained in this
way at such a film thickness that the basecoat hides the area of
damage and tapers off in the adjacent region of the original finish
coated with the coating material from stage (2),
5.) a polymeric film is formed from the composition applied in
stage (4),
6.) a suitable transparent topcoat composition is applied to the
basecoat obtained in this way, if necessary to the parts of the
coating from stage (2) not coated with a basecoat and, if
necessary, to the adjacent original finish, and then
7.) the topcoat, where appropriate together with the basecoat and
where appropriate together with the coating obtained in stage (2)
is dried at temperatures between room temperature and 140.degree.
C., preferably at temperatures below 100.degree. C. and
particularly preferably at temperatures below 80.degree. C.
The repair of areas of damage of a paint finish is usually carried
out by thorough cleaning of the area of damage, sanding, if
necessary applying a surfacer and applying a refinish body filler
to the area of damage. The painting of the area of damage then
follows. However, in a panel repair of this kind, differences in
shade can often be expected. The repair of metallic paints is
particularly difficult, since the shade and brightness of the
special effect are highly dependent on the method of working. The
width of the spray gunnozzle and the spray pressure, inter alia,
play a crucial role here. The method of thinning and the spray
viscosity likewise influence shade and special effect.
If in a panel repair of this kind shade differences are to be
expected and the area is not demarcated by decorative trim or
edges, it may be expedient and economical to compensate the shade
differences by a blend-in of the adjacent area using the so-called
tapering-off technique.
As described in Chapter 7 "Automotive Refinishing" of the Glasurit
Handbook "Pigments and Paints", 11th Edition, Curt R. Vincentz
Verlag Hanover 1984, in the case of metallic multicoat finishes the
repair area and the adjacent parts are resprayed for this purpose
with a conventional, i.e. solvent-borne, highly thinned clearcoat
after the preparative work described above, such as cleaning,
sanding, surfacing, etc. It is important that this clearcoat is
also sprayed on to the repair area, i.e. the body filler patches.
Customary conventional clearcoats, for example 2-component
clearcoats based on hydroxyl-containing acrylate copolymers as
binders and isocyanates as crosslinking agents, are used as the
clearcoat for this purpose.
After the clearcoat coating produced in this way has been
surface-dried at room temperature or a slightly elevated
temperature, the area of damage is resprayed with special-effect
paints, such as metallic basecoats, in such a way that the paint
hides the area of damage and tapers off into the adjacent areas,
i.e. from the edge of the area of damage outwards the film
thickness gradually diminishes to 0 .mu.m. If desired, the edge
zone can in the case of difficult colors be resprayed using lower
spray pressure. Low-solid conventional special-effect paints are
usually employed for this repair of the area of damage.
After the basecoat coating produced in this way has been
surface-dried, the refinish area and the adjacent parts are
completely resprayed with the clearcoat described above and are
dried together with the coats applied before-hand at temperatures
preferably between room temperature and 100.degree. C., after a
flash-off time which may or may not be necessary. Since the
metallic basecoats used in this process contain an extremely high
proportion of up to 90% of organic solvents, the use of aqueous
basecoats is desirable for reasons of economy and to improve work
safety (fire protection) and reduce environmental pollution. In
particular, when the known aqueous basecoats are applied directly,
for this purpose, to an aqueous refinish body filler, the areas of
damage cannot be repaired satisfactorily, since this gives rise to
shade changes and special effect variations in the region of the
area of damage. Repair of the areas of damage using the blend-in
spraying technique described above is likewise not satisfactorily
possible. This is due to the fact that the required tapering-off
spraying into the adjacent part regularly leads to an altered
orientation of the effect-producing pigments and hence to shade
changes and a poor metallic effect in the edge zones (for example
at the transition region between the special-effect basecoat and
the clearcoat), thus again making the refinish area distinctly
visible.
Furthermore, EP-B-104,779 discloses a process for the refinishing
of soft plastic substrates, in which an aqueous polyurethane
coating composition is applied to the plastic surface coated with
repair material and is dried, and subsequently in a further step
conventional, i.e. solvent-borne, pigmented coating materials are
applied. The aqueous polyurethane coating composition provides a
solvent barrier coat which is intended to prevent the damage, such
as blistering, caused by attack by the solvents contained in the
pigmented coating materials.
EP-B-10,007 discloses a process for the refinishing of automotive
bodies, in which a solvent barrier coat is likewise first applied
to the substrate, the protective coat is dried and solvent-borne
automotive refinish paints are then applied. The barrier coat is
produced by applying an alcoholic or aqueous-alcoholic solution of
a polyamide resin. As in the EP-B-104,779 process, this barrier
coat is intended to prevent attack on the substrate by the solvents
contained in the automotive refinish paints applied
subsequently.
Finally, EP-A-320,552 discloses a process for the production of a
multicoat paint system, in which an aqueous coating composition,
preferably containing metallic pigments, is first applied to the
body-filled substrate end dried, after which a conventional aqueous
basecoat is applied, followed by a clearcoat. Application of the
aqueous coating composition prior to the basecoat/clearcoat coating
is intended to achieve, on homogeneous substrates, en enhancement
of the metallic effect, in particular an enhancement of the surface
brightness, especially in the case of the original finish. On the
other hand, the problems of shade changes at the edge zones in the
case of refinish coatings are not described.
The object of the present invention is to provide a process for the
production of a multicoat refinish paint system which process
allows areas of damage to a multicoat metallic finish to be
repaired in such a way that the area of repair is as little visible
as possible, if at all, i.e. that shade changes, clouding and other
blemishes at the edge zones (i.e. the refinish body filler/original
finish transition region and the basecoat/clearcoat transition
region) are avoided. In addition, there should be good adhesion
between the original finish, or the materials employed for the
repair of the area of damage, and the basecoat coating. Above all,
however, for reasons of economy, to reduce environmental pollution
during the drying of the coatings and for reasons of work safety
(fire protection), these requirements should be guaranteed to be
met even when aqueous or water-thinnable basecoats are
employed.
Surprisingly, this object is achieved by the process outlined at
the outset, wherein
I.) an aqueous coating material, containing
a) 5 to 50% by weight, based on the total weight of the coating
material, of at least one water-thinnable or water-dispersible
film-forming material,
b) 0 to 20% by weight, based on the total weight of the coating
material, of at least one organic solvent and
c) conventional auxiliaries and additives, if appropriate,
is applied in stage (2), the dry film thickness of this aqueous
coating material being between 2 and 50 .mu.m the region of the
area of damage, and
II.) an aqueous basecoat composition is applied in stage (4).
Surprisingly, areas of damage to a multicoat metallic finish can be
repaired using the process according to the invention in such a way
that the refinished area is only barely visible, if at all. In
particular, the effects at the edge zone, such as shade changes,
clouding and others, frequently observed with the conventional
refinish processes are avoided. These problems arise neither at the
transition region between the area of damage treated, if
appropriate, with a body filler or surfacer and the area of the
adjacent original finish, nor at the transition region between the
freshly applied refinish metallic basecoat and the original finish.
Of crucial importance is the fact that these outstanding results
can be achieved using aqueous refinish metallic basecoats, so that
above all the environmental pollution arising during the drying of
the paint films is kept low. However, the use of aqueous metallic
basecoats is highly significant also in respect of aspects of work
safety and the economy of this process.
Finally, the process according to the invention guarantees good
adhesion between the original finish, or the materials used for the
repair of the area of damage, and the basecoat.
The process according to the invention for the production of a
multicoat refinish paint system can be employed on a very wide
variety of substrates. It is immaterial whether the systems
exhibiting areas of damage are conventional or water-thinnable.
In order to carry out the process according to the invention the
area of damage is first prepared in the usual way by thorough
cleaning, sanding, if necessary surfacing and body-filling. The
preliminary work necessary in each case depends on the nature of
damage to be repaired and on the required quality of the refinish.
It is known (cf. for example Chapter 7 "Automotive Refinishing" of
Glasurit Handbook "Pigments and Paints", 11th Edition, Curt R.
Vincentz Verlag, Hanover 1984) and therefore need not be elucidated
in greater detail here. Both conventional and water-thinnable base
materials, such as are usually used, are suitable for this
preliminary work.
Water-thinnable base materials are employed increasingly for
reasons of economy, and to improve work safety (fire protection)
and especially to reduce environmental pollution.
It is an essential part of the invention that an aqueous or
water-thinnable coating material is applied to the appropriately
prepared area of damage and, in addition, to the adjacent areas of
the original finish. This coating material is applied in the region
of the area of damage with a dry film thickness of 2 to 50 .mu.m,
preferably 5 to 20 .mu.m. On the other hand, in the adjacent areas
of the original finish the dry film thickness of this coating
material diminishes gradually outwards from the edge of the area of
damage to 0 .mu.m. This type of coating with diminishing film
thickness is usually referred to as the tapering-off technique. For
simplicity's sake this designation is also used below for the
application of coatings at a film thickness which gradually
diminishes to 0 .mu.m. The region of the adjacent original finish
which is coated with this coating material using the tapering-off
technique depends on many factors, for example the spray gun used,
the spraying pressure, the nature, size and position of the area of
damage and similar. The application of the coating material using
the tapering-off technique usually takes place in a region of the
original finish between 1 cm and 1 m wide around the area of
damage. However, the optimum area of the original finish to be
coated in each case may be readily determined by a person skilled
in the art by means of a few routine experiments.
In addition to this variant of applying the coating material by the
tapering-off spray technique it is also possible to apply this
coating material to the area of damage and to the entire adjacent
region of the original finish until a boundary is reached, for
example an edge or a trim, at a dry film thickness of 2 to 50
.mu.m, preferably 5 to 20 .mu.m. This is of significance for those
metallic colors which normally create problems, for example on
account of a low hiding power of the basecoats. It is then
particularly advantageous for the coating material to contain
coloring pigments which allow an improved shade match with the
original finish.
The aqueous or water-thinnable coating materials used in the
process according to the invention contain at least one
water-thinnable or water-dispersible binder, preferably in amounts
from 5 to 50% by weight, particularly preferably in amounts from 10
to 30%, in each case based on the total weight of the coating
material. These binders can be chosen, for example, from the group
of acrylate, polyurethane and/or polyester resins. If appropriate,
they can be modified by functional groups which control the
properties of the resins in a particular direction and/or are
suitable for crosslinking of the resins using curing agents. The
curing agents can be added to the aqueous or water-thinnable
coating material under discussion, but they can also be contained
in the basecoat and/or in the final clearcoat coating.
Suitable binders for these aqueous or water-thinnable coating
materials are, for example, the polyurethane resins described in
DE-OS 3,545,618, DE-OS 3,739,332, U.S. Pat. No. 4,719,132,
EP-A-89,497, DE-OS 3,210,051, DE-OS 2,624,442, U.S. Pat. Nos.
4,558,090, 4,489,135, EP-A-38,127, DE-OS 3,628,124, EP-A-158,099,
DE-OS 2,926,584, EP-A-195,931 and DE-OS 3,321,180.
The water-thinnable polyurethane resins containing urea groups
preferably employed are those which have a number average molecular
weight (determined by gel permeation chromatography using
polystyrene as standard) of 1000 to 25,000, preferably 1500 to
20,000, and an acid value of 5 to 70 mg of KOH/g, preferably 10 to
30 mg of KOH/g, and can be prepared by a reaction, preferably a
chain extension, of prepolymers containing isocyanate groups with
polyamines and/or hydrazine.
The preparation of the prepolymers containing isocyanate groups
takes place by reacting polyalcohols having a hydroxyl value of 10
to 1800, preferably 50 to 500, mg of KOH/g with excess
polyisocyanates in organic solvents which cannot react with
isocyanates, at temperatures of up to 150.degree. C., preferably
50.degree. to 130.degree. C. The equivalence ratio of NCO groups to
OH groups is between 1.5 to 1.0 and 1.0 to 1.0, preferably between
1.4 and 1.2 to 1. The polyols used for the preparation of the
prepolymers may be low-molecular and/or high-molecular and they may
contain slow-reacting anionic groups. In order to increase the
hardness of the polyurethane, low-molecular polyols may be used.
They have a molecular weight of 60 to about 400 and may contain
aliphatic, alicyclic or aromatic groups. Amounts of up to 30% by
weight, preferably about 2 to 20% by weight, of the total polyol
components are used. The low-molecular polyols containing up to
about 20 carbon atoms per molecule, such as ethylene glycol,
diethylene glycol, triethylene glycol, 1,2-propanediol,
1,3-propanediol, 1,4-butanediol, 1,2-butylene glycol,
1,6-hexanediol, trimethylolpropane, castor oil or hydrogenated
castor oil, di(trimethylolpropane)ether, pentaerythritol,
1,2-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A,
bisphenol F, neopentyl glycol, neopentyl glycol ester of
hydroxypivalic acid, hydroxethylated or hydroxypropylated bisphenol
A, hydrogenated bisphenol A and mixtures thereof are advantageous.
In order to obtain an NCO prepolymer of high flexibility, a high
proportion of a predominantly linear polyol having a preferred
hydroxyl value of 30 to 150 mg of KOH/g should be added. Up to 97%
by weight of the total polyol may consist of saturated and
unsaturated polyesters and/or polyethers of a molecular weight Mn
of 400 to 5000. Suitable high-molecular polyols are aliphatic
polyether diols of the general formula H--(--O--(--CHR).sub.n
--).sub.m --OH, in which R is hydrogen or a low alkyl radical,
unsubstituted or substituted with various substituents, n being 2
to 6, preferably 3 to 4 and m being 2 to 100, preferably 5 to 50.
Examples are linear or branched polyether diols, such as
poly(oxyethylene) glycols, poly(oxypropylene) glycols and/or
poly(oxybutylene) glycols. The chosen polyether diols should not
introduce excessive amounts of ether groups, since otherwise the
polymers formed swell in water. The preferred polyether diols are
poly(oxypropylene) glycols of a molecular weight range Mn of 400 to
3000. Polyester diols are prepared by esterification of organic
dicarboxylic acids or their anhydrides with organic diols or are
derived from a hydroxycarboxylic acid or a lactone. To prepare
branched polyether polyols, it is possible to use to a small extent
polyols or polycarboxylic acids of a higher valency. The
dicarboxylic acids and diols may be linear or branched aliphatic,
cycloaliphatic or aromatic dicarboxylic acids or diols. The diols
used for the preparation of the polyesters consist, for example, of
alkylene glycols such as ethylene glycol, propylene glycol,
butylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol
and other diols such as dimethylolcyclohexane. The acid component
of the polyester consists first of all of low-molecular
dicarboxylic acids or their anhydrides containing 2 to 30,
preferably 4 to 18, carbon atoms per molecule. Examples of suitable
acids are o-phthalic acid, isophthalic acid, terephthalic acid,
tetrahydrophthalic acid, cyclohexanedicarboxylic acid, succinic
acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric
acid, glutaric acid, hexachloroheptanedicarboxylic acid,
tetrachlorophthalic acid and/or dimerized fatty acids. Instead of
these acids their anhydrides may be used, where these exist.
Smaller amounts of carboxylic acids containing 3 or more carboxyl
groups, for example trimellitic anhydride or the adduct of maleic
anhydride and unsaturated fatty acids, may also be present in the
formation of polyester polyols. Polyester diols which are obtained
by reacting a lactone with a diol are also used according to the
invention. They are distinguished by the presence of a terminal
hydroxyl group and recurring polyester moieties of the formula
--(--CO--(CHR).sub.n --CH.sub.2 --O--)--, in which n is preferably
4 to 6 and the substituent R is hydrogen or an alkyl, cycloalkyl or
alkoxy radical. No substituent contains more than 12 carbon atoms.
The total number of carbon atoms in the substituents does not
exceed 12 per lactone ring. Corresponding examples are
hydroxycaproic acid, hydroxybutyric acid, hydroxydecanoic acid
and/or hydroxystearic acid.
The lactone used as starting material can be represented by the
following general formula ##STR1## in which n and R have the
meanings already defined. The unsubstituted .epsilon.-caprolactone,
in which n is 4 and all the R substituents are hydrogen, is
preferred for the preparation of the polyester diols. The reaction
with lactone is initiated by low-molecular polyols, such as
ethylene glycol, 1,3-propanediol, 1,4-butanediol and
dimethylolcyclohexane. However, other reaction components, such as
ethylenediumine, alkyldialkanolamines or even urea may also be
reacted with caprolactone.
Suitable high-molecular diols are also polylactam diols which are
prepared by the reaction of, for example, .epsilon.-caprolactam
with low-molecular diols. Aliphatic, cycloaliphatic and/or aromatic
polyisocyanates containing at least two isocyanate groups per
molecule are used as typical multifunctional isocyanates. The
isomers or isomeric mixtures of organic diisocyanates are
preferred. Suitable aromatic diisocyanates are phenylene
diisocyanate, tolylene diisocyanate, xylylene diisocyanate,
biphenylene diisocyanate, naphthylene diisocyanate and
diphenylmethane diisocyanate.
(Cyclo)aliphatic dlisocyanates furnish products with low tendency
to yellowing owing to their good resistance to ultraviolet light.
Corresponding examples are isophorone diisocyanate, cyclopentylene
diisocyanate and the hydrogenation products of aromatic
diisocyanates, such as cyclohexylene diisocyanate,
methylcyclohexylene diisocyanate and dicyclohexylmethane
diisocyanate. Examples of suitable aliphatic diisocyanates are
trimethylene diisocyanate, tetramethylene diisocyanate,
pentamethylene diisocyanate, hexamethylene diisocyanate, propylene
diisocyanate, ethylethylene diisocyanate, dimethylethylene
diisocyanate, methyltrimethylene diisocyanate and trimethylhexane
diisocyanate. Particularly preferred diisocyanates are isophorone
diisocyanate and dicyclohexylmethane diisocyanate.
The polyisocyanate component employed for the formation of the
prepolymer may also contain a proportion of higher-valent
polyisocyanates, provided this does not engender gel formation.
Products which are formed by trimerization or oligomerization of
diisocyanates or by reaction of diisocyanates with polyfunctional
compounds containing OH or NH groups have been found to be suitable
triisocyanates. The biuret of hexamethylene diisocyanate and water,
the isocyanurate of hexamethylene diisocyanate or the adduct of
isophorone diisocyanate and trimethylolpropane, for example, belong
to this group.
The average functionality can be reduced, if desired, by the
addition of monoisocyanates. Examples of such chain-terminating
monoisocyanates are phenyl isocyanate, cyclohexyl isocyanate and
stearyl isocyanate. Polyurethanes are generally incompatible with
water, unless special constituents are incorporated in their
synthesis and/or special preparative steps are taken. Thus an acid
value is incorporated which is high enough for the neutralized
product to be dispersible in water to yield a stable dispersion.
Compounds suitable for this purpose are those containing two
H-active groups reactive with isocyanates and at least one group
capable of anion formation. Suitable groups reactive with
isocyanate groups are in particular hydroxyl groups and primary
and/or secondary amino groups. Groups capable of anion formation
are carboxyl, sulfonic acid and/or phosphonic acid groups.
Carboxylic acid groups or carboxylate groups are preferred. Their
reactivity should be so low that the isocyanate groups of the
diisocyanate preferably react with the other groups of the molecule
reactive toward isocyanate groups. Alkanoic acids containing two
substituents on the carbon atoms in the .alpha. position are used
for this purpose. The substituent may be a hydroxyl group, an alkyl
group or an alkylol group. These polyols comprise at least one,
generally 1 to 3 carboxyl groups in the molecule. They have two to
about 25, preferably 3 to 10, carbon atoms. Examples of such
compounds are dihydroxypropionic acid, dihydroxysuccinic acid and
dihydroxybenzoic acid. A group of dihydroxyalkanoic acids which is
particularly preferred are the .alpha.,.alpha.-dimethylolalkanoic
acids which are characterized by the structural formula RC(CH.sub.2
OH).sub.2 COOH, in which R is hydrogen or an alkyl group containing
up to about 20 carbon atoms. Examples of such compounds are
2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid,
2,2-dimethylolbutyric acid and 2,2-dimethylolpentanoic acid. The
preferred dihydroxyalkanoic acid is 2,2-dimethylolpropionic acid.
Examples of compounds containing amino groups are diaminovaleric
acid, 3,4-diaminobenzoic acid, 2,4-diaminotoluenesulfonic acid and
2,4-diaminodiphenyl ether sulfonic acid. The polyol containing
carboxyl groups may amount to 3 to 100% by weight, preferably 5 to
50% by weight, of the total polyol content in the NCO prepolymer.
The amount of ionizable carboxyl groups available as salt by
neutralization of the carboxyl groups is generally at least 0.4% by
weight, preferably at least 0.7% by weight, based on the solid. The
upper limit is about 6% by weight. The amount of dihydroxyalkanoic
acids in the non-neutralized prepolymers furnish an acid value of
at least 5, preferably at least 10. The upper limit for the acid
value is about 70, preferably about 40 mg of KOH/g, based on the
solid.
This dihydroxyalkanoic acid is advantageously at least partially
neutralized with a tertiary amine prior to the reaction with
isocyanates in order to prevent a reaction with the
isocyanates.
The NCO prepolymers used according to the invention may be prepared
by a simultaneous reaction of the polyol or polyol mixture with an
excess of diisocyanate. Alternatively, the reaction may also take
place in the prescribed sequence in stages. Examples are described
in DE-OS 2,624,442 AND DE-OS 3,210,051. The reaction temperature is
up to 150.degree. C., a temperature in the region from 50.degree.
to 130.degree. C. being preferred. The reaction is allowed to
proceed until virtually all hydroxyl functions have reacted.
The NCO prepolymer contains at least about 0.5% by weight of
isocyanate groups, preferably at least 1% by weight of NCO, based
on the solid. The upper limit is about 15% by weight, preferably
10% by weight, particularly preferably about 5% by weight.
The reaction may be carried out, if appropriate, in the presence of
a catalyst, such as organotin compounds and/or tertiary amines. In
order to keep the coreactants in a liquid state and allow better
temperature control during the reaction, organic solvents which are
free of active hydrogen according to Zerewitinoff may be added.
Examples of suitable solvents are dimethylformamide, esters, ethers
such as diethylene glycol dimethyl ether, ketoesters, ketones such
as methyl ethyl ketone and acetone, ketones substituted by methoxy
groups, such as methoxyhexanone, glycol ether esters,
chlorinatedhydrocarbons, aliphatic and alicyclic hydrocarbon
pyrrolidones, such as N-methylpyrrolidone, hydrogenated furans,
aromatic hydrocarbons and mixtures thereof. The amount of solvents
can fluctuate within wide limits and should be sufficient to allow
the formation of a prepolymer solution of suitable viscosity. In
most cases 0.01 to 15% by weight of solvent, preferably 0.02 to 8%
by weight of solvent, based on the solid, is sufficient. If the
solvents, whether water-soluble or water-insoluble, have a boiling
point lower than that of water, they may be carefuly distilled off
by vacuum-distillation or by thin-layer evaporation subsequent to
the preparation of the urea-containing polyurethane dispersion.
Higher-boiling solvents should be water-soluble, and remain in the
aqueous polyurethane dispersion to facilitate the coalescence of
the polymer particles during film formation. N-methylpyrrolidone,
possibly in a mixture with ketones such as methyl ethyl ketone, is
particularly preferred as a solvent.
The anionic groups of the NCO prepolymer are neutralized at least
partially with a tertiary amine. The increase in water
dispersibility produced by this means is sufficient to provide for
an infinite thinnability. It is also sufficient to disperse the
neutralized polyurethane containing urea groups to form a stable
dispersion. Examples of suitable tertiary amines are
trimethylamine, triethylamine, dimethylethylamine,
diethylmethylamine and N-methylmorpholine. The NCO prepolymer is
thinned with water after neutralization and then yields a fine
dispersion. Shortly afterwards the isocyanate groups which are
still present are reacted with dimmines and/or polyamines
containing primary and/or secondary amino groups as chain
extenders. This reaction leads to a further union and to an
increase in molecular weight. To achieve optimum properties, the
competing reaction between amine and water with the isocyanate must
be well regulated (duration, temperature, concentration) and well
supervised to achieve reproducible production. Water-soluble
compounds are preferred as chain extenders, because they increase
the dispersibility of the polymeric end product in water. Hydrazine
and organic dimmines are preferred, because they usually form the
highest molecular weight without causing the resin to gel. It is
assumed, of course, that the ratio of the amino groups to the
isocyanate groups has been chosen appropriately. The amount of the
chain extender is determined by its functionality, by the NCO
content of the prepolymer and by reaction time. The ratio of the
active hydrogen atoms in the chain extender to the NCO groups in
the prepolymer should usually be less than 2:1 and preferably in
the range of 1.0:1 to 1.75:1. The presence of excess active
hydrogen, especially in the form of primary amino groups, may lead
to polymers with undesirably low molecular mass.
The polyamines are essentially alkylene polymmines of 1 to 40
carbon atoms, preferably about 2 to 15 carbon atoms. They can carry
substituents which contain no hydrogen atoms capable of reacting
with isocyanate groups. Examples of these are polyamines having a
linear or branched aliphatic, cycloaliphatic or aromatic structure
and at least two primary amino groups. Suitable diamines are
ethylenediamine, propylenediamine, 1,4-butylenediamine, piperazine,
1,4-cyclohexyldimethylamine, 1,6-hexamethylenediamine,
trimethylhexamethylenediamine, methanediamine, isophoronediamine,
4,4'-diaminodicyclohexylmethane and aminoethylethanolamine.
Preferred diamines are alkyldiamines or cycloalkyldiamines such as
propylenediamine and
1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane. The chain
extension can be carried out at least partially using a polyamine
which contains at least three amine groups having a reactive
hydrogen. This type of polyamine may be used in such an amount that
after the extension of the polymer unreacted aminic nitrogen atoms
having 1 or 2 reactive hydrogen atoms are present. Such suitable
polyamines are diethylenetriamine, triethylenetetramine,
dipropylenetriamine and dibutylenetriamine. Preferred polyamines
are the alkyltriamines or cycloalkyltriamines, such as
diethylenetriamine. To prevent gel formation in the chain
extension, small amounts of monoamines, such as ethylhexylamine,
may also be added.
The water-thinnable polyurethane resins to be used according to the
invention and the preparation thereof are also described in
EP-A-89,497 and U.S. Pat. No. 4,719,132. However, other known
water-thinnable or water-dispersible polyurethane resins which are
obtained, for example, by reacting the prepolymers containing
isocyanate groups and described above with triols and/or polyols
instead of polyamines are also suitable binders. Such
water-thinnable polyurethane resins and the preparation thereof are
described, for example, in U.S. Pat. No. 4,423,179 and DE-OS
3,739,322.
Examples of polyols containing at least three hydroxyl groups are
trimethylolpropane, glycerol, erythritol, mesoerythritol, arabitol,
adonitol, etc. Trimethylolpropane is used for preference. The
reaction of the prepolymer with the triols and/or polyols is
preferably controlled by the stoichiometry of the compounds
employed, in such a way that chain extensions occur.
The water-thinnable coating materials to be used according to the
invention employ particularly advantageously as binder a
water-thinnable emulsion polymer which can be obtained by
(a) polymerizing in a first stage 10 to 90 parts by weight of an
ethylenicallyunsaturated monomer or of a mixture of ethylenically
unsaturated monomers in aqueous phase in the presence of one or
more emulsifiers and one or more radical-forming initiators, the
ethylenicallyunsaturated monomer or the mixture of ethylenically
unsaturated monomers being chosen so that in the first stage a
polymer is obtained having a glass transition temperature
(T.sub.G1) of +30.degree. to +110.degree. C. and,
(b) after at least 80% by weight of the ethylenically unsaturated
monomer or monomer mixture used in the first stage have reacted,
polymerizing in a second stage 90 to 10 parts by weight of an
ethylenically unsaturated monomer or of a mixture of ethylenically
unsaturated monomers in the presence of the polymer obtained in the
first stage, the monomer used in the second stage or the mixture of
ethylenically unsaturated monomers used in the second stage being
chosen so that a sole polymerization of the monomer used in the
second stage or of the mixture of ethylenically unsaturated
monomers used in the second stage furnishes a polymer having a
glass transition temperature (T.sub.G2) of -60.degree. to
+20.degree. C., and the reaction conditions being chosen so that
the resultant emulsion polymer has a number average molecular
weight of 200,000 to 2,000,000, and the type and amount of the
ethylenically unsaturated monomer or mixture of monomers used in
the first stage and those of the ethylenically unsaturated monomer
or mixture of monomers used in the second stage being chosen so
that the resultant emulsion polymer has a hydroxyl value of 2 to
100 mg of KOH/g and the difference T.sub.G1 -T.sub.G2 is 10.degree.
to 170.degree. C.
The water-thinnable emulsion polymers used according to the
invention can be prepared by a two-stage emulsion polymerization in
an aqueous medium in known equipments, for example in a stirred
reaction vessel fitted with heating and cooling facilities. The
addition of the monomers can be carried out in such a way that a
solution consisting of the total water, the emulsifier and some of
the initiator is introduced into the reaction vessel and the
monomer or mixture of monomers and, separately but at the same
time, the remainder of the initiator are slowly added at the
temperature of polymerization. It is also possible, however, to
charge the reaction vessel with some of the water and emulsifier
and to prepare from the remainder of the water and emulsifier and
from the monomer or mixture of monomers a pre-emulsion which is
slowly added at the temperature of polymerization, the initiator
again being added separately.
It is preferred in the first stage to add the monomer or mixture of
monomers in the form of a pre-emulsion and in the second stage to
add the monomer or mixture of monomers as such, i.e. without water
and emulsifier, and to add the initiator separately but at the same
time. It is particularly preferred in the first stage to prepare
first a seed polymer from some (usually about 30% by weight of the
total of the pre-emulsion to be used) of the pre-emulsion to he
used in the first stage and then add the remainder of the
pre-emulsion to be used in the first stage.
The polymerization temperature is generally in the range from
20.degree. to 100.degree. C., preferably 40.degree. to 90.degree.
C.
The proportions between the amount of monomers and the amount of
water can be chosen so that the resultant dispersion has a solids
content of 30 to 60% by weight, preferably 35 to 50% by weight.
An anionic emulsifier is preferably used, either alone or in a
mixture.
Examples of anionic emulsifiers are the alkali metal salts of
sulfuric acid hemiesters of alkylphenols or alcohols, and also the
sulfuric acid hemiesters of oxethylated alkylphenols or oxethylated
alcohols, preferably the alkali metal salts of the sulfuric acid
hemiester of a nonylphenol, alkylsulfonate or arylsulfonate which
has been reacted with 4-5 mol of ethylene oxide per mol, sodium
lauryl sulfate, sodium lauryl ethoxylate sulfate and secondary
sodium alkanesulfonates whose carbon chain contains 8-20 carbon
atoms. The amount of the anionic emulsifier is 0.1-5.0% by weight,
based on the monomers, preferably 0.5-3.0% by weight. Furthermore,
to raise the stability of the aqueous dispersions, a non-ionic
emulsifier of an ethoxylated alkylphenol or fatty alcohol, for
example an addition product of 1 mol of nonylphenol and 4-30 mol of
ethylene oxide in a mixture with the anionic emulsifier, may be
additionally used.
A peroxide compound is preferably used as the free-radical-forming
initiator. The initiator is water-soluble or monomer-soluble. A
water-soluble initiator is used for preference.
Suitable initiators are the customary inorganic percompounds such
as ammonium persulfate, potassium persulfate, ammonium or alkali
metal peroxydiphosphate, and organic peroxides such as benzoyl
peroxide, organic peresters such as perisopivalate, partly in
combination with reducing agents such as sodium disulfite,
hydrazine, hydroxylamine and catalytic amounts of an accelerator
such as iron, cobalt, cerium and vanadyl salts. Alkali metal or
ammonium peroxydisulfates are used for preference. The redox
initiator systems, disclosed in EP-A-107,300, may also be used.
In the first stage 10 to 90, preferably 35 to 65, parts by weight
of an ethylenically unsaturated monomer or of a mixture of
ethylenicallyunsaturated monomers are emulsion polymerized. The
monomer or mixture of monomers used in the first stage is chosen so
that when polymerization of the monomer or mixture of monomers used
in the first stage is allowed to reach completion, a polymer having
a glass transition temperature (T.sub.G1) of +30.degree. C. to
110.degree. C., preferably 60.degree. to 95.degree. C., is
obtained. Since the glass transition temperature of emulsion
polymers can be approximately calculated from the equation ##EQU1##
a person skilled in the art has no difficulties in choosing the
monomer or mixture of monomers to be used in the first stage in
such a way that when polymerization of the monomer or mixture of
monomers used in the first stage is allowed to reach completion, a
polymer having a glass transition temperature (T.sub.G1) of
+30.degree. to +110.degree. C., preferably 60.degree. to 95.degree.
C., is obtained.
Examples of monomers which can be used in the first stage are the
following: vinylaromatic hydrocarbons, such as styrene,
.alpha.-alkylstyrene and vinyltoluene, esters of acrylic acid or
methacrylic acid, in particular aliphatic and cycloaliphatic
acrylates or methacrylates having up to 20 carbon atoms in the
alcohol radical, such as methyl, ethyl, propyl, butyl, hexyl,
ethylhexyl, stearyl, lauryl and cyclohexyl acrylate or
methacrylate, acrylic and/or methacrylic acid, acrylamide and/or
methacrylamide, N-methylolacrylamide and/or
N-methylolmethacrylamide, hydroxyalkyl esters of acrylic acid,
methacrylic acid or another .alpha.,.beta.-ethylenicallyunsaturated
carboxylic acid, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl
acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate,
3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate,
4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate etc.
Ethylenicallyunsaturated monomers or mixtures of ethylenically
unsaturated monomers which are essentially free from hydroxyl and
carboxyl groups are preferably employed in the first stage. The
expression "essentially free" is intended to signify that it is
preferred to use monomers or monomeric mixtures which are free from
hydroxyl and carboxyl groups, but that the monomers or mixtures of
monomers used may also comprise small amounts (for example due to
impurities) of hydroxyl and/or carboxyl groups. The content of
hydroxyl and carboxyl groups should preferably be at most such that
a polymer prepared from the monomer or mixture of monomers used in
the first stage has an OH value of not more than 5 mg of KOH/g and
an acid value of not more than 3 mg of KOH/g.
The first stage employs particularly preferably a mixture
consisting of
(a1) 100 to 60%, preferably 99.5 to 75%, by weight of a
cycloaliphatic or aliphatic ester of methacrylic or acrylic acid or
a mixture of such esters and
(a2) 0 to 40%, preferably 0.5 to 25%, by weight of a monomer which
is copolymerizable with (a1) or a mixture of such monomers,
the total weight of (a1) and (a2) being always 100% by weight.
The following, for example, can be used as component (a1):
cyclohexyl acrylate, cyclohexyl methacrylate, alkyl acrylates and
alkyl methacrylates having up to 20 carbon atoms in the alkyl
radical, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl,
stearyl and lauryl acrylate and methacrylate or mixtures of these
monomers.
Vinylaromatic hydrocarbons such as styrene, .alpha.-alkylstyrene
and vinyltoluene, acrylamide, methacrylamide, acrylonitrile and
methacrylonitrile or mixtures of these monomers may be used, for
example, as component (a2).
After at least 80% by weight, preferably at least 95% by weight, of
the ethylenically unsaturated monomer or mixture of monomers used
in the first stage have reacted, 90 to 10, preferably 65 to 35,
parts by weight of an ethylenically unsaturated monomer or a
mixture of ethylenically unsaturated monomers are emulsion
polymerized in a second stage in the presence of the polymer
obtained in the first stage, the monomer or mixture of monomers
used in the second stage being chosen so that a sole polymerization
of the monomer or mixture of monomers used in the second stage
furnishes a polymer having a glass transition temperature
(T.sub.G2) of -60.degree. to +20.degree. C., preferably -50.degree.
to 0.degree. C. This choice poses no difficulties to a person
skilled in the art, since the glass transition temperatures of
emulsion polymers--as already stated above--can readily be
approximately calculated. It is furthermore an essential part of
the invention that the type and amount of the monomer or mixture of
monomers used in the first stage and those of the monomer or
mixture of monomers used in the second stage are chosen so that the
resultant emulsion polymer has a hydroxyl value of 2 to 100 mg of
KOH/g, preferably of 10 to 50 mg of KOH/g, and the difference
T.sub.G1 -T.sub.G2 is 10.degree. to 170.degree. C., preferably
80.degree. to 150.degree. C.
Examples of monomers which can be used in the second stage are the
following: vinylaromatic hydrocarbons such as styrene,
.alpha.-alkylstyrene and vinyltoluene, esters of acrylic or
methacrylic acid, in particular aliphatic and cycloaliphatic
acrylates or methacrylates having up to 20 carbon atoms in the
alcohol radical, such as methyl, ethyl, propyl, butyl, hexyl,
ethylhexyl, stearyl, lauryl and cyclohexyl acrylate or
methacrylate, acrylic and/or methacrylic acid, acrylamide and/or
methacrylamide, N-methylolacrylamide and/or
N-methylolmethacrylamide, hydroxyalkyl esters of acrylic acid,
methacrylic acid or another .alpha.,.beta.-ethylenicallyunsaturated
carboxylic acid, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl
acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate,
3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate,
4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, etc.
The second stage employs preferably a mixture consisting of
(b1) 47 to 99, preferably 75 to 90, % by weight of a cycloaliphatic
or aliphatic ester of methacrylic or acrylic acid or a mixture of
such esters,
(b2) 1 to 20, preferably 5 to 15, % by weight of a
hydroxyl-containing monomer which is copolymerizable with (b1),
(b3) and (b4) or a mixture of such monomers,
(b3) 0 to 8, preferably 2 to 6, % by weight of a carboxyl- or
sulfonic acid-containing monomer which is copolymerizabIe with
(b1), (b2) and (b4) or a mixture of such monomers and
(b4) 0 to 25, preferably 2 to 15, % by weight of a further monomer
which is copolymerizable with (b1), (b2) and (b3) or a mixture of
such monomers,
the total weight of (b1), (b2), (b3) and (b4) being always 100% by
weight.
Cyclohexyl acrylate, cyclohexyl methacrylate, alkyl acrylates and
alkyl methacrylates having up to 20 carbon atoms in the alkyl
radical, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl,
stearyl and lauryl acrylate and methacrylate or mixtures of these
monomers may be used, for example, as component (b1).
Hydroxyalkyl esters of acrylic acid, methacrylic acid or another
ethylenicallyunsaturated carboxylic acid may be used, for example,
as component (b2). These esters may be derived from an alkylene
glycol which is esterified with the acid, or they can be obtained
by a reaction of the acid with an alkylene oxide. Hydroxyalkyl
esters of acrylic and methacrylic acid, in which the hydroxyalkyl
group contains up to 4 carbon atoms, or mixtures of these
hydroxyalkyl esters, are preferably used as the component (b2).
Examples of these hydroxyalkyl esters are 2-hydroxyethyl acrylate,
2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl
methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl
methacrylate, 4-hydroxybutyl acrylate or 4-hydroxybutyl
methacrylate. Corresponding esters of other unsaturated acids, such
as ethacrylic acid, crotonic acid and similar acids having up to
about 6 carbon atoms per molecule may also be used.
Acrylic acid and/or methacrylic acid and/or
acrylamidoethylpropanesulfonic acid are preferably used as
component (b3). However, other ethylenically unsaturated acids
having up to 6 carbon atoms in the molecule may also be used.
Examples of such acids are ethacrylic acid, crotonic acid, maleic
acid, fumaric acid and itaconic acid.
Vinylaromatic hydrocarbons such as styrene, .alpha.-alkylstyrene
and vinyltoluene, acrylamide, methacrylamide, acrylonitrile and
methacrylonitrile or mixtures of these monomers may be used, for
example, as component (b4).
The emulsion polymer used according to the invention should have a
number average molecular weight (determination by gel permeation
chromatography using polystyrene as standard) of 200,000 to
2,000,000, preferably 300,000 to 1,500,000 and, usually, acid
values below 100 mg of KOH/g and OH values of 2 to 100 mg of KOH/g.
If the emulsion polymer contains no or only very few acid groups
(acid value below 3 mg of KOH/g, for example), it is advantageous
to add to the coating composition a carboxyl-containing resin, for
example a carboxyl-containing polyurethane, polyester or
polyacrylate resin. The amounts of the carboxyl-containing resin
are to be chosen so that the acid value of the mixture of emulsion
polymer and carboxyl-containing resin is 10 mg of KOH/g or
greater.
A person skilled in the art knows how he must choose the reaction
conditions during the emulsion polymerization so as to obtain
emulsion polymers having the number average molecular weights
indicated above (cf. for example "Chemistry, Physics and Technology
of Plastics in Individual Articles, Dispersions of synthetic high
polymers", Part 1 by F. Holscher, Springer Verlag, Berlin,
Heidelberg, N.Y., 1969).
It is finally also possible to use as the film-forming material a
mixture consisting of less than 100 to 40% by weight of the
emulsion polymer described above and of up to 60% by weight of the
polyurethane resin described above, the amounts being in each case
based on the solids content and their total always being 100% by
weight.
If appropriate, the aqueous coating materials used according to the
invention may advantageously contain, besides the emulsion polymer
or the mixture of emulsion polymers and polyurethane resin, further
compatible water-thinnable resins, such as amino resins, polyesters
and polyethers which generally act as grinding resins for the
pigments.
The aqueous coating materials used according to the invention may
contain, if appropriate, 5 to 20% by weight, based on the total
solids content of the coating material, of a water-thinnable amino
resin, preferably melamine resin, and 5 to 20% by weight of a
water-thinnable polyether (for example polypropylene glycol having
a number average molecular weight of 400 to 900).
Any other known water-thinnable or water-dispersible resin, for
example based on acrylate copolymers and polyester resins, either
alone or in a mixture, may of course be employed in the aqueous
coating materials used according to the invention as film-forming
material. In addition to the film-forming material, the aqueous or
water-thinnable coating materials also contain organic solvents in
the usual amounts, preferably 0 to 20% by weight of solvent, based
on the total weight of the coating material. Examples of suitable
solvents are alcohols, such as butyl glycol, ethoxypropanol,
ethanol, propanol, ketones, such as methyl ethyl ketone and methyl
isobutyl ketone, and hydrocarbons such as various Solvesso.RTM.
grades and Solvent Naphtha.RTM..
Moreover, the aqueous coating materials also contain water in
customary amounts, preferably 30 to 95% by weight of water, based
on the total weight of the coating material.
If appropriate, the aqueous coating materials may also contain
further customary auxiliaries and additives in the usual amounts,
for example fillers, non-pigmented, transparent fillers such as
silicon dioxide, phyllosilicates, barium sulfate and others being
preferably used. The fillers are preferably used in amounts of, if
appropriate, 0 to 20% by weight, based on the total weight of the
coating material. If appropriate, the aqueous coating materials may
also contain further customary paint additives in the usual
amounts, preferably 0 to 5% by weight, based on the total weight of
the coating material. Thus conventional additives for the
enhancement of substrate wetting, film formation, adhesion to the
substrate, antifoam action and/or rheology control may in
particular be added.
The coating materials used according to the invention are
preferably employed as clearcoat. Where the coating materials are
used to coat a large area of the original finish between
boundaries, they may also contain coloring pigments which allow a
better shade match. These pigments are preferably used in amounts
from 0 to 20% by weight, based on the total weight of the coating
material. Examples of suitable coloring pigments are inorganic
pigments such as titanium dioxide, iron oxide, carbon black, etc.,
and organic pigments such as phthalocyanine, quinacridone and
similar pigments.
However, the aqueous coating materials contain no metallic pigments
and no non-metallic special-effect pigments.
In a second stage an aqueous coating composition is applied to this
first coating after formation of a polymeric film, preferably after
previous drying of this first coating at temperatures between room
temperature and 140.degree. C., preferably at temperatures below
80.degree. C., during a period of 5 to 60 min. and, if appropriate,
after a brief cooling period of up to 10 min. In this operation
this aqueous or water-thinnable basecoat composition is applied to
the area of damage in such a way that it hides the latter, i.e. no
shade difference is noticeable between the coating and the
substrate, and is applied to the adjacent area, presprayed with the
aqueous coating material described above, by the tapering-off spray
technique, i.e. its film thickness diminishes from the edge of the
area of damage in the direction of the outer edge. Overlapping of
the original finish, i.e. applying the basecoat beyond the region
of the first coating, must be avoided in order to avoid marking the
region of the edge zone by altered orientation of the metallic
pigment. If in the first stage of the process the total part area
has been coated with the aqueous coating material, then the total
part area can also be hidingly coated with the basecoat. The dry
film thickness of the basecoat is generally between 5 and 50 .mu.m
in the region of the area of damage.
Any aqueous basecoat composition which is curable at low
temperatures, generally from room temperature to about 140.degree.
C., preferably at temperatures below 80.degree. C., is suitable for
use in the process according to the invention. Aqueous basecoat
compositions which contain as the film-forming material the
emulsion polymer described above, preparable by the two-stage
emulsion polymerization process likewise already described, are
particularly preferred. For details regarding the properties and
preparation of this emulsion polymer reference is therefore made
only to pages 23 to 34 of the present description. This emulsion
polymer is usually employed in the basecoat compositions in amounts
of 5 to 50% by weight, preferably of 5 to 25% by weight, based in
each case on the total weight of the basecoat composition.
It is also possible to use as the film-forming material in the
basecoat compositions the water-thinnable or water-dispersible
polyurethane resins likewise already described. For details
concerning the properties and preparation of these polyurethane
resins reference should be made to pages 11 to 23 of the present
description. These polyurethane resins are usually employed in the
basecoat compositions in amounts of 1 to 40% by weight, preferably
of 3 to 25% by weight, based on the total weight of the basecoat
composition.
The aqueous basecoat compositions may also contain as the
film-forming material a mixture of preferably less than 100 to 40%
by weight of the emulsion polymer described above and preferably 9
to 60% by weight of the polyurethane resin described above, the
amounts being based in each case on the solids content and their
total being always 100% by weight. In addition, the basecoat
compositions contain, in each case in the customary amounts,
organic solvents, water, conventional auxiliaries and additives if
appropriate, coloring pigments and metallic and/or special effect
pigments.
The basecoat compositions may contain as pigments coloring
inorganic pigments such as titanium dioxide, iron oxide, carbon
black, etc., organic coloring pigments and customary metallic
pigments (for example commercial aluminum bronzes, stainless steel
bronzes . . . ) and non-metallic special-effect pigments (for
example nacreous luster or interference pigments). The basecoat
compositions preferably contain metallic pigments and/or
special-effect pigments. The degree of pigmentation is in the
customary ranges, preferably 0 to 10% by weight, based on the total
weight of the basecoat composition.
Furthermore, crosslinked polymeric microparticles, such as those
disclosed in EP-A-38,127, and/or customary rheological inorganic or
organic additives may be added to the basecoat compositions in
usual amounts, for example 0.05 to 6% by weight, based on the total
weights of the basecoat composition. Thus, examples of thickeners
used are inorganic phyllosilicates such as aluminum-magnesium
silicates, sodium-magnesium phyllosilicates and
sodium-magnesium-fluorine-lithium phyllosilicates of the
montmorillonite type, water-soluble cellulose ethers such as
hydroxtethyl cellulose, methylcellulose or carhoxymethylcellulose
and synthetic polymers comprising ionic and/or associatively acting
groups such as polyvinyl alcohol, poly(meth)acrylamide,
poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic
anhydride or ethylene-maleic anhydride copolymers and derivatives
thereof or hydrophobically modified ethoxylated urethanes or
polyacrylates. A combination consisting of a carboxyl-containing
polyacrylate copolymer having an acid value of 60 to 780,
preferably 200 to 500, mg of KOH/g and a
sodium-magnesiumphyllosilicate is particularly preferred. Basecoat
compositions which are particularly preferred and have improved
humidity resistance of the coatings are obtained when when the
sodiummagnesium phyllosilicate is used in the form of an aqueous
paste. Pastes which are particularly preferred contain either 3% by
weight of phyllosilicate and 3% by weight of polypropylene glycol
or 2% by weight of phyllosilicate and 2% by weight, based in each
case on the total weight of the paste, of other commercial
surfactants.
The basecoat compositions generally have a solids content of about
5 to 50% by weight, preferably 10 to 25% by weight.
The coating compositions may in addition contain usual organic
solvents. The amount of these should be kept as low as possible. It
is, for example, below 15% by weight.
The pH of the basecoat compositions is generally adjusted to
between 6.5 and 9.0. The adjustment of the pH may be carried out
using conventional amines, such as ammonia, triethylamine,
dimethylaminoethanol and N-methylmorpholine.
However, other known basecoat compositions, for example those
systems described in GB-A-2,073,609 and EP-A-195,931, are also
suitable for use in the process according to the invention.
After the formation of a polymeric film on the basecoat
composition, preferably after drying of the basecoat at
temperatures from room temperature up to 140.degree. C., preferably
at temperatures below 80.degree. C., for a period of 5 to 60 min.,
and, if appropriate, after a brief cooling period of generally at
least 5 minutes, a suitable transparent topcoat composition is
applied to the basecoat and--should the whole of the first coat not
be provided with a basecoat--to the possibly still uncoated parts
of the first coat. The topcoat composition is preferably applied so
as to taper off into the uncoated region of the original finish or
to the whole of the adjacent original finish up to an edge,
decorative trim or similar in such a way that the original finish
is hidden, since in this way time-consuming polishing work is
eliminated. The dry film thickness of the topcoat is generally
between 30 and 100 .mu.m. 1- or 2-component clearcoats, both
organic solvent-borne and aqueous, are suitable as the topcoat
composition. Clearcoats based on a hydroxyl-containing acrylate
copolymer and a blocked polyisocyanate are frequently used. Such
clearcoats are disclosed, for example, in the patent applications
DE 3,412,534, DE 3,609,519, DE 3,731,652 and DE 3,823,005. The
moisture-curing clearcoats based on polyaddition polymers
containing alkoxysilane or acryloxysilane units described in the
international patent application with the international publication
number WO88/02010 are likewise suitable. After a flash-off time of
about 5 minutes, if necessary, the topcoat, where appropriate
together with the basecoat and where appropriate together with the
coating obtained in stage (2) is dried at temperatures between room
temperature and 140.degree. C., preferably at temperatures below
80.degree. C., for a period of 5 to 120 min.
The invention is explained in greater detail in the examples below.
All parts and percentages are by weight, unless expressly stated
otherwise. A multicoat original finish, such as is customary in
automotive production line painting, is used as the substrate. It
is unimportant whether the finishes are conventionally based or
based on water-thinnable systems.
1. Simulation of an area of damage
1.1 Simulation of an area of damage 1
A steel panel, primed by the electro-dipping process, which is
furnished with a commercial conventional body filler based on a
melamine-crosslinked polyester resin (FC 60-7133 from BASF Lacke
+Farben AG, Munster; dry film thickness 40 .mu.m), a commercial
conventional metallic basecoat based on cellulose acetobutyrate (AE
54-9153 from BASF Lacke+Farben AG, Munster; dry film thickness 15
.mu.m) and a commercial conventional clearcoat based on
isocyanate-crosslinked hydroxyl-containing acrylates (AF 23-0185
from BASF Lacke+Farben AG; dry film thickness 60 .mu.m), is used as
the substrate. After the customary drying (60.degree. C., 30 min.)
the coated panel is additional stored for several hours at elevated
temperature, for example 60.degree. C., and the finish is thus
aged. A refinish area is simulated on this substrate by producing
an area with the paint abraded to bare metal (diameter.apprxeq.5
cm). This abraded area is produced in such a way that the
transitions from metal to clearcoat are as flat as possible.
A commercial conventional refinish primer surfacer, based on
isocyanate-crosslinked hydroxyl-containing acrylates (AB 85-1122
from BASF Lacke+Farben AG, Munster; dry film thickness 70 .mu.m) is
applied to the area of damage thus produced and is dried by heating
at 60.degree. C. for a period of 30 min.
The area of damage and the parts of the original finish adjacent to
the area of damage which are also to be painted in the course of
the blend-in spray technique (a strip at least 1 cm wide around the
area of damage) are sanded down using abrasive paper in such a way
that smooth transitions to the original finish are produced.
1.2 Simulation of an area of damage 2
Using a method similar to that used to produce the area of damage
1, a further area of damage 2 is simulated which differs from the
area of damage 1 only in that an aqueous refinish body filler based
on an acrylate dispersion (AB 76-1986 from BASF Lacke+Farben AG,
Munster; dry film thickness 70 .mu.m) is applied to the abraded
area produced instead of the conventional refinish body filler, and
is dried.
2. Preparation of water-thinnable coating materials
2.1 Coating material 1 based on polyurethane
An aqueous coating material 1 is prepared by a method similar to
that used in Example 3 of DE-OS 3,210,051, but with the difference
that the coating material contains no aluminum pigment and no
melamine resin.
As described in DE-OS 3,210,051 for the polyurethane dispersion 3,
the polyurethane dispersion used in the coating material 1 is
prepared as follows:
500 g of a polypropylene glycol having a hydroxyl value of 112 are
freed from water in vacuo at 100.degree. C. for 1 hour. 262 g of
4,4'-dicyclohexylmethane diisocyanate are added at 80.degree. C.,
and the reaction mixture is stirred at 90.degree. C. until the
isocyanate content is 5.47% by weight, based on the total
weight.
A solution of 33.5 g of dimethylolpropionic acid and 25 g of
triethylamine in 200 g of N-methylpyrrolidone is added to the
reaction mixture, cooled to 60.degree. C., which is then stirred
for 1 hour at 90.degree. C. The resultant mass is transferred into
1650 g of deionized water with vigorous stirring. 40 g of a 15%
hydrazine solution are then added to the resultant dispersion in
the course of 20 minutes with stirring. The resultant dispersion
has a solids content of 32% and an efflux time of 23 seconds in a
DIN Cup No. 4.
As described in DE-OS 3,210,051 the water-soluble polyester used is
prepared as follows:
832 parts by weight of neopentyl glycol are introduced into a
reaction vessel fitted with a stirrer, a thermometer and a packed
column, and are melted. 664 parts by weight of isophthalic acid are
added. Heat is applied with stirring at such a rate that the
temperature at the head of the column does not exceed 100.degree.
C. Esterification is allowed to proceed at a temperature not higher
than 220.degree. C., until an acid value of 8.5 is reached. 384
parts by weight of trimellitic anhydride are added to the reaction
mixture cooled to 180.degree. C., and esterification is allowed to
proceed until an acid value of 39 is reached. The mixture is
diluted with 425 parts by weight of butanol.
Using a method similar to that used in DE-OS-3,210,051, the
thickener used is prepared as follows:
A 3% paste of a sodium-magnesium-fluorine-lithium silicate in
water: To prepare the paste, the silicate is stirred into water
over 30-60 minutes using a dissolver and the mixture is allowed to
stand overnight. Next day it is stirred for a further 10 to 15
minutes.
For the preparation of the coating material 1, 25 parts of the
thickener described above are added with stirring to 25 parts of
the polyurethane dispersion (32% solids) described above using a
method similar to that used in Example 3 of DE-OS 3,210,051. 5
parts of the polyester resin (80% solids) described above, 0.5
parts of dimethylethanolamine (10% solution in water), 5 parts of
butyl glycol and 32.5 parts of water are added with further
stirring. After the mixture has been stirred for 30 minutes, its
viscosity is adjusted with water to an efflux time of 16 to 25
seconds in a DIN No. 4 cup.
2.2 Coating material 2 based on polyurethane
An aqueous coating material 2 is prepared using a method similar to
that used in Example 5 of DE-OS 3,210,051, but with the difference
that the coating material contains no aluminum pigment and no
melamine resin.
The polyurethane dispersion used in the coating material 2 is
prepared using a method similar to that used for the polyurethane
dispersion 5 of DE-OS 3,210,051 as follows:
650 g of a commercial polyether obtained from tetrahydrofuran,
having a hydroxyl value of 173, are freed from water in vacuo at
100.degree. C. for 1 hour. 533 g of isophorone diisocyanate are
added at 80.degree. C., and the reaction mixture is then stirred at
90.degree. C. until the isocyanate content is 9.88% by weight,
based on the total weight. A solution of 93 g of
dimethylolpropionic acid and 70 g of triethylamine in 400 g of
N-methylpyrrolidone is added to the reaction mixture cooled to
60.degree. C., which is then stirred for 1 hour at 90.degree. C.
The resultant polyurethane mass is stirred into 4700 g of cold
deionized water with vigorous stirring. 120 g of a 15% hydrazine
solution are then added to the resultant dispersion in the course
of 20 minutes. The resultant dispersion has a solids content of 19%
and an efflux time of 27 seconds in a DIN No. 4 cup.
The acrylate resin used is prepared as follows:
400 parts by weight of n-butanol are introduced into a reaction
vessel fitted with a stirrer, thermometer and reflux condenser and
are heated to 110.degree. C. A mixture of 1000 parts by weight of
n-butyl methacrylate, 580 parts by weight of methyl methacrylate,
175 parts by weight of 2-hydroxyethyl acrylate and 175 parts by
weight of acrylic acid is then added from one feed vessel, and a
mixture of 80 parts by weight of t-butyl perbenzoate and 80 parts
by weight of n-butanol are added from a second feed vessel, the
additions being carried out uniformly and simultaneously over a
period of 4 hours. The temperature during the addition is kept at
110.degree. C. After the addition, polymerization is allowed to
proceed further at 110.degree. C. and after 1 hour a mixture of 10
parts by weight of t-butyl perbenzoate and 10 parts by weight of
n-butanol is added. After a further 1.5 hours a polymer solution is
obtained which has a solids content of 79.7% by weight, an acid
value of 64.0, based on the solids content, and a viscosity of 850
mPas measured in a plate-cone viscometer at a solids content of 60%
by weight in n-butanol.
A paste, 3% in water, of a sodium-magnesium phyllosilicate is used
as a thickener.
For the preparation of the coating material 2, 30 parts of the
polyurethane dispersion (19% solids) described above are added with
stirring to 25 parts of the thickener described above using a
method similar to that used in Example 5 of DE-OS 3,210,051. 6
parts of the acrylate resin (80% solids) described above, 0.5 part
of dimethylethanolamine (10% in water), 5 parts of butyl glycol and
26.5 parts of water are added with further stirring. After the
mixture has been stirred for 30 minutes, its viscosity is adjusted
with water to an efflux time of 16 to 25 seconds in a DIN No. 4
cup.
2.3 Coating material 3 based on an emulsion polymer
An emulsion polymer dispersion 1 is first prepared as follows:
1344 g of deionized water and 12 g of a 30% aqueous solution of the
ammonium salt of penta(ethylene glycol)nonyl phenyl ether sulfate
(Fenopon.RTM. EP 110 from GAF Corp., emulsifier 1) are introduced
into a cylindrical double-walled glass vessel fitted with a
stirrer, reflux condenser, stirrable feed vessel, dropping funnel
and thermometer, and the mixture is heated to 82.degree. C. In the
stirrable feed vessel an emulsion is prepared from 720 g of
deionized water, 24 g of emulsifier 1, 10.8 g of acrylamide, 864 g
of methyl methacrylate and 216 g of n-butyl methacrylate. 30% by
weight of this emulsion is added to the contents of the
double-walled flask. 28% by weight of a solution of 3.1 g of
ammoniumperoxodisulfate in 188 g of deionized water are then added
dropwise in the course of 5 minutes. An exothermic reaction sets
in. The reaction temperature is kept between 82.degree. and
88.degree. C. 15 minutes after the addition of the ammonium
peroxodisulfate solution has been completed, the remaining 70% by
weight of the emulsion together with the remaining 72% by weight of
the ammoniumperoxodisulfate solution are added over one hour, the
temperature being kept at 85.degree. C. The reaction mixture is
then cooled to 82.degree. C. and treated in the course of 2 hours
with a mixture of 842 g of n-butyl acrylate, 108 g of hydroxypropyl
methacrylate, 43 g of methyl methacrylate, 43.2 g of methacrylic
acid, 32.4 g of acrylamide and 5.4 g of eicosa(ethhlene glycol)
nonyl phenyl ether (Antarox.RTM. CO 850 from GAF Corp., emulsifier
2) and 343 g of deionized water. After the addition is completed,
the reaction mixture is allowed to stand at 85.degree. C. for a
further 1.5 hours. It is then cooled and the dispersion is passed
through a 30 .mu.m mesh fabric. A finely divided dispersion is
obtained having a non-volatile content of 45% by weight, a pH of
3.4, an acid value of 13 mg of KOH/g and an OH value of 20 mg of
KOH/g.
For the preparation of the coating material 3, the pH of 50 g of
the emulsion polymer dispersion 1 is adjusted to 6.9 with ammonia
and is treated with 9.4 g of a 3.5% solution of a commercial
polyacrylic acid thickener (Viscalex.RTM. HV 30 from Allied
Colloids, pH 8.0) and with 0.5 g of a commercial antifoam (BYK.RTM.
035). The pH of the resultant mixture is adjusted to 7.0 by the
addition, if appropriate, of a 25% aqueous ammonia solution. 60 g
of a preswelled aqueous paste, containing 2% by weight of an
inorganic sodium-magnesium phyllosilicate thickener and 2% by
weight, based on the weight of the paste, of polypropylene glycol
(number average molecular weight=900) are added to this mixture
with stirring. The viscosity is then adjusted to an efflux time of
16-25 seconds in a DIN No. 4 cup by the addition of deionized
water.
2.4 Coating material 4 based on an emulsion polymer
An emulsion polymer dispersion 2 is first prepared as follows:
1344 g of deionized water and 12 g of a 40% aqueous solution of the
ammonium salt of penta(ethylene glycol) nonyl phenyl ether sulfate
(Fenopon.RTM. EP 110 from GAF Corp., emulsifier 1) are introduced
into a cylindrical double-walled glass vessel fitted with a
stirrer, reflux condenser, stirrable feed vessel, dropping funnel
and thermometer and are heated to 80.degree. C. An emulsion is
prepared in the stirrable feed vessel from 720 g of deionized
water, 24 g of emulsifier 1, 10.8 g of acrylamide, 518 g of methyl
methacrylate, 292 g of n-butyl methacrylate and 205 g of styrene.
30% by weight of this emulsion are added to the mixture in the
double-walled glass vessel. A solution of 0.9 g of ammonium
peroxodisulfate (APS) in 55 g of deionized water is added dropwise
over 5 minutes. An exothermic reaction sets in. The reaction
temperature is kept between 80.degree. and 85.degree. C. 15 minutes
after the addition of the above APS solution has been completed, a
solution of 2.2 g of APS in 480 g of water is added in the course
of 3 hours and the remaining 70% of the above emulsion is added in
the course of one hour, the reaction temperature being kept at
80.degree. C. When the addition of the emulsion has been completed,
the reaction mixture is cooled to 77.degree. C. and a mixture of
745 g of n-butyl acrylate, 119 g of methyl methacrylate, 108 g of
hydroxypropyl methacrylate, 54 g of styrene, 42.7 g of ethylhexyl
acrylate, 42.7 g of methacrylic acid, 21.6 g of acrylamide and 2.2
g of emulsifier 2 is added in the course of 2 hours.
When the addition has been completed, the reaction mixture is kept
at 80.degree. C. for a further 1.5 hours. It is then cooled and the
dispersion is passed through a 30 .mu.m mesh fabric. A fine
dispersion is obtained having a non-volatile content of 45% by
weight, a pH of 3.8, an acid value of 13 mg of KOH/g and an OH
value of 19 mg of KOH/g.
The preparation of coating material 4 is carried out using a method
similar to that used for the preparation of coating material 3,
with the sole difference that 50 g of the emulsion polymer
dispersion 2 is used instead of 50 g of the emulsion polymer
dispersion 1.
2.5 Coating material 5 based on polyurethane
First, a polyurethane dispersion 3 is prepared as follows:
686.3 g of a polyester having a number average molecular weight of
1400 based on a commercially available unsaturated dimeric fatty
acid (having an iodine number of 10 mg of I.sub.2 /g, a maximum
monomer content of 0.1%, a maximum trimer content of 2%, an acid
number of from 195 to 200 mg of KOH/g and a saponification number
of from 197 to 202 mg of KOH/g), isophthalic acid and hexanediol
are introduced under a protective gas into a suitable reaction
vessel fitted with stirrer, reflux condenser and feed vessel, and
10.8 g of hexanediol, 55.9 g of dimethylolpropionic acid, 344.9 g
of methyl ethyl ketone and 303.6 g of
4,4'-di(isocyanatocyclohexyl)methane are added one after the other.
This mixture is kept under reflux until the isocyanate content has
dropped to 1.0%. 26.7 g of trimethylolpropane are subsequently
added to the mixture, which is kept under reflux until a viscosity
of 12 dPas has been reached (for a partial solution of 1:1=resin
solution/N-methylpyrrolidone).
Any excess isocyanate present is destroyed by addition of 47.7 g of
buryl glycol. 32.7 g of dimethylethanolamine, 2688.3 g of
demineralized water and 193.0 g of butyl glycol are subsequently
added to the reaction mixture with vigorous stirring. Removal of
the methyl ethyl ketone by vacuum distillation gives a dispersion
having a solids content of about 27%.
In order to prepare the coating material 5, 30 parts of the
above-described polyurethane dispersion 3 (solids content 27% ) are
added with stirring to 25 parts of the above-described thickener. 6
parts of the acrylate resin (solids content 80% ), 0.5 parts of
dimethylethanolamine (10% in water), 5 parts of butyl glycol and
26.5 parts of water are added with further stirring. After the
mixture has been stirred for 30 minutes, its viscosity is adjusted
with water to an efflux time of from 16 to 25 s in a DIN No. 4
cup.
3. Preparation of aqueous basecoat compositions
3.1 Basecoat composition 1
A basecoat composition 1 is prepared as follows using a method
similar to that used in Example 3 of DE-OS 3,210,051:
25 parts of the polyurethane dispersion (32% solids) described in
2.1 are added with stirring to 25 parts of the thickener described
in 2.1.5 parts of the polyester resin (80% solids) described in
2.1, 0.5 part of dimethylethanolamine (10% solution in water), 2
parts of a commercial methanol-etherified melamine-formaldehyde
resin (solids content 70% in water), 5 parts of a commercial
aluminum pigment paste (aluminum content 60 to 65%, average
particle diameter 10 .mu.m), 5 parts of butyl glycol and 32.5 parts
of water are added with further stirring. After the mixture has
been stirred for 30 minutes, its viscosity is adjusted with water
to an efflux time of 16 to 25 seconds in a DIN No. 4 cup.
3.2 Basecoat composition 2
A basecoat composition 2 is prepared as follows by a method similar
to that used in Example 5 of DE-OS 3,210,051:
30 parts of the polyurethane dispersion (19% solids) described in
2.2 are added with stirring to 25 parts of the thickener described
in 2.2.6 parts of the acrylate resin (80% solids) described in 2.2,
0.5 part of dimethylethanolamine (10% in water), 2 parts of a
commercial methanol-etherified melamine-formaldehyde resin (solids
content 70% in water), 5 parts of a commercial aluminum pigment
paste (aluminum content 60 to 65%, average particle diameter 10
.mu.m), 5 parts of butyl glycol and 26.5 parts of water are added
with further stirring. After the mixture has been stirred for 30
minutes, its viscosity is adjusted with water to an efflux time of
16 to 25 seconds in a DIN No. 4 cup.
3.3 Basecoat composition 3
The basecoat composition 3 is prepared as follows:
8.0 g of butyl glycol and 4.5 g of an aluminum bronze according to
DE-OS 3,636,183 (aluminum content 60 to 65% by weight) are stirred
for 15 minutes using a high-speed stirrer at 300-500 rpm. A mixture
1 is obtained.
The pH of 50 g of the emulsion polymer dispersion described in 2.3
is adjusted to 6.9 with ammonia, and this is treated with 9.4 g of
a 3.5% solution of a commercial polyacrylic acid thickener
(Viscalex.RTM. HV 30 from Allied Colloids, pH 8.0) and 0.5 g of a
commercial antifoam (BYK.RTM. 035). The mixture 2 is obtained. For
the preparation of the basecoats according to the invention the
mixtures 1 and 2 are mixed for 30 minutes at 800-1000 rpm and the
pH is then adjusted to 7.0, if appropriate, using a 25% aqueous
ammonia solution. 60 g of a pre-swelled aqueous paste, containing
2% by weight of inorganic sodium-magnesiumphyllosilicate thickener
and 2% by weight, based on the weight of the paste, of
polypropylene glycol (number average molecular weight=900) are
added to this mixture with stirring. The viscosity is then adjusted
with deionized water to an efflux time of 16-25 seconds in a DIN
No. 4 cup.
3.4 Basecoat composition 4
The basecoat composition 4 is prepared using a method similar to
that used for basecoat composition 3, with the sole difference that
50 g of the emulsion dispersion 2 described in 2.4 are used instead
of 50 g of the emulsion polymer dispersion 1.
3.5 Basecoat composition 5
30 parts of the polyurethane dispersion (solids content 27% )
described in 2.5 are added to 25 parts of the thickener described
in 2.2.6 parts of the acrylate resin (solids content 80% )
described in 2.2, 0.5 part of dimethylethanolamine (10% in water),
2 parts of a commercially available methanol-etherified
melamineformaldehyde resin (solids content 70% in water), 5 parts
of a commercially available aluminum pigment paste (aluminum
content from 60 to 65%, mean particle diameter 10 .mu.m), 5 parts
of butyl glycol and 26.5 parts of water are added with further
stirring. After the mixture has been stirred for 30 minutes, its
viscosity is adjusted with water to an efflux time of from 16 to 25
s in a DIN No. 4 cup.
4. Topcoat compositions used
4.1 Clearcoat 1
The commercial 2-component clearcoat based on
isocyanate-crosslinked hydroxyl-containing acrylates (AF 23-0185
plus SC 29-0173 plus SV 41-0391 from BASF Lacke+Farben AG, Munster;
mixing ratio 2: 1: 0.6) is used.
4.2 Clearcoat 2
A commercial, highly thinned 2-component clearcoat 2 is used which
differs from clearcoat 1 only by the mixing ratio of the
components. The mixing ratio of clearcoat 2 is 2:1:27.
EXAMPLES 1 TO 4
The areas of damage 1 and 2 described in 1 are resprayed (SATA jet
spray gun, nozzle width 1.4 mm, spray pressure 4 bar) beyond the
body-filled area into the abraded clearcoat of the original finish
(in a strip at least 1 cm wide around the area of damage) with the
aqueous coating materials 2.1 to 2.4. A just continuous paint film
of low thickness is to be produced. The measured dry film
thicknesses of this coat were 5 .mu.m. The coating materials were
dried under the conditions stated in Table 1. The aqueous basecoat
compositions 3.1 to 3.4 are then sprayed on (SATA jet spray gun,
nozzle width 1.4 mm, spray pressure 2-3 bar). These water-thinnable
metallic basecoats are applied to the area of damage in such a way
that they hide the latter (dry film thickness 15 .mu.m), and are
applied to the adjacent area presprayed with the aqueous coating
material by the tapering-off spray technique. Overlapping of the
unpretreated original finish by the basecoat must be avoided in
order to avoid marking in the region of the edge zone by altered
orientation of the metallic pigments. After a brief flash-off time
of 60 min. in the case of basecoat compositions 1 and 2 and 30 min.
in the case of basecoat compositions 3 and 4 the clearcoat is
applied to the entire refinish area and beyond the region of the
applied aqueous coating material using the tapering-off spray
technique into the region of the unpretreated original finish.
Applying the clearcoat beyond the region of the basecoat into the
adjacent parts achieves a uniform surface structure, so that costly
polishing work at the area of damage is no longer necessary. In
this operation the clearcoat is applied in the region of the area
of damage at a dry film thickness of 60 .mu.m. After a brief
flash-off time of 5 min. the topcoat is then dried at 60.degree. C.
for 30 min. The resulting coat structure in each case and its
application properties are listed in Table 1. After suitable drying
of the aqueous coating material an outstanding repair of the area
of damage is obtained in all cases. No shade changes, no
alterations of the metallic effect, no clouding and no similar
phenomena were observed especially in the edge zone region (both at
the boundary between the refinish body filler and the original
finish and at the boundary between the basecoat and the aqueous
coating material from the first process stage). The shade match
with the original finish is very good, and furthermore there are no
problems regarding adhesion between the original finish and the
refinish paint system.
Comparison Examples 1 to 3
Methods similar to those used in Examples 1 to 4 are used, with the
sole difference that no aqueous coating material is applied but the
basecoat is applied directly to the prepared (body-filled) area of
damage and to the adjacent regions. In all cases only an inadequate
repair of the area of damage was possible, since shade changes and
in particular effect alterations occurred especially in the
transition region between basecoat and original finish.
The resulting coat structure in each case and its application
properties are listed in Table 2.
Comparison Examples 4 and 5
Methods similar to those used in Examples 1 to 4 are used, with the
sole difference that the conventional, highly thinned clearcoat 2
is applied beyond the area of damage instead of the aqueous coating
material under otherwise identical conditions. Here, too, only an
inadequate repair of the area of damage was possible. The resulting
coat structure in each case and its application properties are
listed in Table 2.
EXAMPLES 5 AND 6
Methods similar to those used in Examples 1 to 4 are used, with the
sole difference that coating material 2.5 and basecoat 3.5 are now
employed in each case.
The layer structure resulting in each case and the applicational
properties thereof are shown in Table 3. In all cases, excellent
refinishing of the damaged area is obtained after suitable drying
of the aqueous coating material. Especially in the transition
region (both at the boundary between the repair filler and the
original finish and at the boundary between the basecoat and the
aqueous coating material in the first process step), no changes in
shade, changes in the metallic effect, cloud formation, and the
like are observed. Shade matching to the original finish is very
good, and in addition there are no adhesion problems between the
original finish and the refinish.
TABLE 1 ______________________________________ Example 1 2 3 4
______________________________________ Area of damage 1 1 2 2
Coating material.sup.1) 2.1 or 2.2 2.3 or 1.4 2.1 or 2.2 2.3 or 2.4
Basecoat.sup.2) 3.1 to 3.4 3.1 to 3.4 3.1 to 3.4 3.1 to 3.4
Clearcoat.sup.3) 4.1 4.1 4.1 4.1 Transition body- pass pass pass
pass filler/orig. finish.sup.4) Edge zone basecoat/ coating
material.sup.5) A pass pass pass pass B fail pass fail pass
______________________________________ Notes on Table 1 .sup.1) the
aqueous coating material used in each case .sup.2) the aqueous
basecoat composition used in each case .sup.3) the topcoat
composition used in each case .sup.4) transition body
filler/original finish both after drying of the aqueous coating
material for 10 min. at 80.degree. C. and after drying of the
aqueous coating material for 10 min. at 20.degree. C.: pass = no
markings, no clouding or similar phenomena .sup.5) transition
basecoat composition/aqueous coating material after different
methods of drying the aqueous coating material: A: drying for 10
min. at 80.degree. C. B: drying for 10 min. at 20.degree. C. pass =
no marking, no clouding or similar phenomena fail = marking of the
edge zone, clouding or similar phenomena
TABLE 2 ______________________________________ C1 C2 C3 C4 C5
______________________________________ Area of damage 1 2 2 1 2
Coating material.sup.1) -- -- -- 4.2 4.2 Basecoat.sup.2) 3.1 to 3.1
or 3.3 or 3.1 to 3.4 3.1 to 3.4 3.4 3.2 3.4 Clearcoat.sup.3) 4.1
4.1 4.1 4.1 4.1 Transition body- pass fail pass pass pass
filler/orig. finish.sup.4) Edge zone fail fail fail fail fail
basecoat/ coating material.sup.5)
______________________________________ Notes on Table 2 .sup.1) the
aqueous coating material used in each case .sup.2) the aqueous
basecoat composition used in each case .sup.3) the topcoat
composition used in each case .sup.4) transition body
filler/original finish: pass = no marking, no clouding or similar
phenomena; fail = marking of the edge zone, clouding or similar
phenomena. .sup.5) transition basecoat composition/original finish
for Comparison Examples 1 to 3 and transition basecoat
composition/coating material 4.2 for Comparison Examples 4 and 5:
pass = marking, no clouding or similar phenomena fail = marking of
the edge zone, clouding or similar phenomena
TABLE 3 ______________________________________ Example 5 6
______________________________________ Area of damage 1 2 Coating
material.sup.1) 2.5 2.5 Basecoat.sup.2) 3.5 3.5 Clearcoat.sup.3)
4.1 4.1 Transition body pass pass filler/orig. finish.sup.4) Edge
zone basecoat/ coating material.sup.5) A pass pass B fail fail
______________________________________ Notes on Table 3 .sup.1) the
aqueous coating material used in each case .sup.2) the aqueous
basecoat composition used in each case .sup.3) the topcoat
composition used in each case .sup.4) transition body
filler/original finish both after drying of the aqueous coating
material for 10 minutes at 80.degree. C. and after drying the
aqueous coating material for 10 minutes at 20.degree. C.: pass = no
marking, clouding or similar phenomena .sup.5) transition basecoat
composition/aqueous coating material after various drying of the
aqueous coating material: A: drying for 10 minutes at 80.degree. C.
B: drying for 10 minutes at 20.degree. C. pass = no marking,
clouding or similar phenomena fail = marking of the edge zone,
clouding or similar phenomena
* * * * *